The present invention relates to an ultrasound diagnostic apparatus for taking an image of an inspection object such as an organ in a living body by transmitting and receiving an ultrasonic beam to generate an ultrasound image used for inspection and diagnosis of the inspection object, a signal processing method, and a recording medium.
Conventionally, ultrasound diagnostic apparatuses such as ultrasound image diagnostic apparatuses using ultrasound images are put to practical use in the medical field.
Generally, this type of ultrasound diagnostic apparatus has an ultrasound probe (hereinafter, also referred to as “probe”) with a plurality of built-in elements (ultrasound transducers) and an apparatus main body connected with the probe. In the ultrasound diagnostic apparatus, an ultrasonic beam is transmitted from the plurality of elements of the probe toward a subject (an inspection object) so as to form a predetermined focus point (transmission focus point), an ultrasonic echo from the subject is received by the probe, and an ultrasound image is generated by electrically processing the reception signal of the received ultrasonic echo in the apparatus main body.
Typically, in ultrasound diagnosis apparatuses, as the transmission frequency when transmitting ultrasonic beams is increased, the distance resolution is improved, but there is a greater degree of attenuation. That is, it is known that although the image quality is better as the transmission frequency is higher, there is a decrease in sensitivity.
Accordingly, the transmission frequency of the ultrasound probe is set to a transmission frequency suitable for a region (depth) to be viewed for each probe according to the purpose thereof, such as a probe for inspecting the surface of body, or a probe for inspecting an abdomen or a heart.
In addition, ultrasound probes capable of switching between transmission frequencies are also used. Using an ultrasound probe capable of switching between transmission frequencies, imaging is carried out at a high frequency when viewing a shallow region, and imaging is carried out at a low frequency when viewing a deep region. Accordingly, shallow regions can be imaged with a higher image quality and deep regions can also be appropriately imaged by suppressing decreases in sensitivity.
In the meantime, the ultrasonic beam is transmitted by the plurality of elements being driven on the basis of a predetermined transmission delay pattern so as to form a set focus point. Such an ultrasonic beam is shaped to be wide in the lateral direction. Therefore, there is a problem in that information on a reflection point located at a position shifted in the lateral direction is picked up and reproduced on the ultrasound image as a so-called ghost signal.
To solve such a problem, in formation of one ultrasound image, the ultrasound diagnostic apparatus superimposes a plurality of data (element data or reception data) obtained by each transmission according to reception times or positions of the elements to correct the data, which is so-called multi-line processing (JP 2009-240700 A). For the ghost signals, even when data is superimposed according to the reception time or the position of the elements, it is possible to eliminate the ghost signals because the ghost signals are superimposed in a shifted state and cancel each other out.